p-Nitrobenzyl esters of various cephalosporins are well known stable crystalline compounds and their cleavage by Zn/HCl (U.S. Pat. No. 3,781,282), Zn/AcOH (U.S. Pat. No. 3,925,372), Zn/thiophenol (GB 1,582,960), sodium dithionite (U.S. Pat. No. 3,799,924) and Pd/C (JACS 96, 4986, 1974) have been recently described. However such methods, especially Zn/HCl for the cleavage of p-nitrobenzyl esters, result in the concomitant production of an insoluble material which complicates the isolation and recovery of the desired cephalosporin carboxylic acids. It is accordingly an objective of the present invention to provide an improved process for converting p-nitrobenzyl ester of cephalosporin to the corresponding cephalosporin carboxylic acid using Fe/HCl in high yield and quality. This novel method has not been found so far in the literature.